Conventional wind turbine towers typically include a tubular pole or a lattice structure to support a wind turbine at a considerable height to capture wind energy. The tubular pole configuration is relatively more simple and easier to assemble than the lattice structure. However, tubular poles use more steel than the lattice structure, resulting in a cost disadvantage with rising prices of steel.
The lattice structure towers use significantly less steel and other materials as compared to conventional tubular towers (generally about 30%-40% less). The lattice towers, however, lack the torsional rigidity of the tubular constructions and this decreased torsional stiffness potentially induces vibrations and stresses in the tower that must be compensated for.
It is known in the civil engineering and construction arts to incorporate damping devices and materials in structures to reduce vibrations, harmonics, and the like. An effective and practical means of damping lattice frame wind towers, however, has not been achieved. In fact, the conventional practice of rigid connections (e.g. bolt or weld connections) at the numerous joints between the vertical structural elements (“legs”) and the cross braces that extend between the legs, as well as at the intersection of the cross braces, may even exacerbate the vibrations and resulting stresses. Vibrations caused by wind against the wind turbine tower may even loosen bolted connections over time.
Accordingly, an improved means for providing effective and practical damping to a lattice frame wind tower, without detracting from the inherent benefits of the structure as compared to tubular towers, is desired.